Correlation ratio measured by Planck from the Half Mission (HM) maps at 217 GHz and 353 GHz, compared to the simulated ratio using PySM dust and CMB templates at the same frequencies. The blue and orange dots represent the expected R_ℓ for the CMB and a single MBB dust emission, with constant (d0) or varying pixel-by-pixel (d1) spectral indices, respectively. Note that the dots are so close that they overlap in the figure. The green envelope shows the range of R_ℓ obtained from 500 realizations of dust LOS frequency de-correlation with ℓ_corr = 10. The black dots are from Fig. 2 of Planck Collaboration Int. L (2017), the gray dots are from Fig. B.2 of Planck Collaboration XI (2020), and the red point is obtained from the values in the middle plot of the second row in Fig. 18 of Planck Collaboration XI (2020).